UPDATE 1-Iran tanker in standoff with West heads to Greece, Iran warns U.S.

DUBAI, Aug 19 (Reuters) - An Iranian tanker caught in a standoff between Tehran and the West was sailing to Greece on Monday after leaving Gibraltar, and Iran warned against any U.S. move to seize the vessel after the British territory rejected a U.S. request to detain it.

Iran's foreign ministry said a U.S. attempt to seize the oil tanker would have "heavy consequences" and a senior Iranian lawmaker said the crisis with Britain would only end after the vessel reached its destination.

British Royal Marines seized the tanker near Gibraltar in July on suspicion it was carrying oil to Syria, a close ally of Iran, in violation of European Union sanctions. That led to heightened tensions on international oil shipping routes through the Gulf.

The Grace 1, renamed the Adrian Darya 1, left anchorage off Gibraltar around 11 p.m. (2100 GMT) on Sunday. Refinitiv ship tracking data showed early on Monday that the vessel was heading to Kalamata in Greece.

The tanker's detention ended last week but a federal court in Washington on Friday issued a warrant for the seizure of the tanker, the oil it carries and nearly $1 million.

Gibraltar said on Sunday it could not comply with that request because it was bound by EU law. (Reporting by Dubai newsroom and Harshith Aranya in Bengaluru; Editing by Neil Fullick)